1. Field of the Invention
The present invention relates to an apparatus for introducing gases into a processing chamber and a method of cleaning the components of the apparatus. More particularly, the present invention relates to a gas distribution plate for introducing gases into a processing chamber and a method for electrically isolating components of the gas distribution plate to form a plasma within the gas distribution plate to thereby effectively perform an in situ clean of the surfaces within the gas distribution plate by plasma enhanced chemical reactions.
2. Background of the Related Art
Chemical vapor deposition (CVD) is a process often used in the fabrication of integrated circuits to form thin films on the surface of substrates or to etch films therefrom. CVD processes, such as those used in the fabrication of integrated circuits, are carried out in process chambers which typically include a gas distribution assembly through which gases are introduced into the process chamber. Gas distribution assemblies are commonly utilized in CVD chambers to uniformly distribute gases over the substrate surface upon their introduction into the chamber. Uniform gas distribution is necessary to enhance uniform deposition characteristics on the surface of a substrate positioned in the chamber for processing.
Generally, a gas distribution assembly includes a grounded gas inlet manifold connected to a gas source to provide gases to a process chamber. The gas inlet manifold inlets gases into a gas gas diffuser to uniformly introduce gases into the CVD chamber above a substrate surface. Referring to FIG. 1, a gas diffuser system 10 communicates directly with the CVD chamber and typically includes a gas injection cover plate 14, a blocker plate 40, and a face plate 33 to evenly disperse gases inlet from a single gas feed line over at least the area of the substrate while minimizing turbulent gas flow. The blocker plate 40 is generally a flat, annular plate member having a plurality of very small apertures or holes passing therethrough to disperse the gas inlet therein uniformly into a space above the face plate 33. The gas is typically inlet from a single gas line wherein the reactant and carrier gases have been mixed, thereby providing a high concentration of gas over the center of the blocker plate 40 at a localized area. The face plate 33 is also a generally flat, annular member having a plurality of apertures or holes, larger than the apertures of the blocker plate 40, through which the gases pass or diffuse to provide a uniform concentration of gases evenly over the substrate.
As further shown in FIG. 1, the face plate 33 is typically disposed below the blocker plate 40 and at least partially forms the upper boundary of the processing region 76 of the chamber. Accordingly, the gases flow through the small apertures of the blocker plate 40 and subsequently through the apertures of the face plate 33 and into the chamber where they undergo plasma assisted chemical reactors. A substrate is typically positioned within the chamber on a substrate support member 72. The gas diffuser 10 is electrically biased by an RF power source 15 to generate a plasma in processing region 76. Precursor gases are inlet through the cover plate 14 and flow into the region 41 above the blocker plate 40. The gases are then dispersed above the blocker plate 40 and pass through the apertures formed in the blocker plate and into a space 78 above the face plate 33. The gases are then further dispersed over the upper surface of the face plate 33 and pass through the apertures formed in the face plate to uniformly distribute the gases over the surface of the substrate where the gases react with one another and deposit on the substrate.
Problems have arisen in utilizing the currently available gas distribution plates and other gas inlet means when the gases undergo unwanted chemical reactions in the gas distribution plate or gas inlet means and deposit therein, typically blocking the small passages of the inlet means, such as the small apertures formed in the blocker plate 40 or even the larger apertures of a face plate 33. The apertures formed in the blocker plate 40 are typically smaller than the apertures formed through the face plate 33 and are much more easily clogged by deposition of reactant gases which are introduced through the gas injection cover plate 14. As a result, the apertures formed through the blocker plate 40 may become clogged following about 1000 to 2000 deposition cycles. These deposits are particularly troubling since the gas diffuser system 10 facilitates uniform deposition of film layers on the substrates by evenly distributing the gases over the surface of the substrate. The rate of buildup of material within the gas diffuser system 10 can be substantially greater than in other areas of the chamber due to the high concentration of precursor and reactant gases and the close proximity of the plasma. After further repetitive CVD processes, the deposits will eventually clog the apertures in the gas diffuser system 10 and require a system shutdown so that the gas diffuser system can be replaced. A system shutdown is very costly due to the downtime and, in addition, a gas diffuser system which cannot be cleaned must be replaced which increases the manufacturing cost.
It would be desirable to clean the gas distribution assembly including the gas diffuser system 10 without the need to remove the gas diffuser system from the chamber, such as when a routine plasma cleaning operation is performed in the chamber. In situ cleaning of the internal chamber walls is typically accomplished by introducing reactive cleaning gases into the chamber, grounding the chamber walls, applying an RF voltage to the gas diffuser system 10 to generate a plasma between the gas diffuser system 10 and the substrate support member 72, and using the plasma to enhance the reaction between the cleaning gases and the material deposited on the surfaces within the chamber . Reaction products are formed which can easily be exhausted from the chamber. During this cleaning process, the face plate 33 may be at least partially cleaned because the plasma is generated adjacent to the face plate allowing the chemical reaction between the cleaning gases and the deposition material formed on the face plate to occur. However, the blocker plate 40, as well as other components of the gas diffuser system 10, are isolated from the plasma region. Therefore, the typical in situ chamber cleaning process is not effective at cleaning material which is deposited within the gas diffuser system 10, especially the small apertures in the blocker plate 40.
Presently, there does not exist an effective self-cleaning blocker plate or a method of cleaning a blocker plate in situ. As a result, the entire gas diffuser system must be removed and replaced. Therefore, there is a need for an apparatus for introducing gases into a processing chamber and a method for in situ cleaning of gas inlet components which are typically isolated from the plasma region within a chamber and are susceptible to build up of deposition material thereon. It would be desirable if the apparatus were simple and economical to reduce manufacturing costs.